1. Field of the Invention
The present invention concerns a method of establishing belt pullout in an occupant restraint system for vehicles and an occupant restraint system for vehicles.
2. Description of the Related Art
Modern motor vehicles are equipped with a series of active and passive safety systems. In that respect active safety systems intervene directly in the driving characteristics of the vehicle while passive safety systems are intended to ensure protection for the occupants from injury in the event of an accident. Active safety systems are for example the anti-locking system for brakes or electronic driving dynamics regulation. Passive safety systems include for example vehicle zones which in the event of an accident are subject to defined deformation (so-called crumple zones). An important group of passive safety systems is represented by the occupant restraint systems. They provide for minimising the risk of injury to occupants in the event of an accident, for example by means of safety belts and/or inflatable impact bags, referred to as airbags.
Safety belts are intended to prevent the body of a vehicle occupant being thrown excessively far forward during an accident and for example hitting against the steering wheel. Modern safety belts are fitted with belt pretensioners which in the event of an accident pull the belt taut and lock it in order to reliably prevent uncontrolled forward displacement. If however the restraint action of the belt is excessively strongly pronounced, the belt itself can cause a loading on the occupant to be restrained, and that loading can give rise to injuries. Such injuries can occur for example in the chest region of the occupant.
In order to avoid injuries due to the belts, force limiters are therefore installed in modern vehicles, which in the case of an accident limit the force acting between the belt and the vehicle occupant by allowing a defined belt pullout which is defined by way of a given force-travel relationship. The force-travel relationship is for example such that pullout of the belt is prevented until the force operative between the belt and the vehicle occupant reaches a predetermined force which is generally about 4 kN. When that force is reached defined belt pullout then takes place in such a way that the force acting on the occupant does not exceed the predetermined force.
The described force limiters are generally designed for standardised vehicle occupants, referred to as 50%-ers. A 50%-er is a person who is 1.80 m tall and weighs 75 kg. Height and weight of such a person correspond to a person who represents precisely the average of the population, that is to say one half of the population is taller and heavier and the other half is shorter and lighter. In the event of an impact against a rigid wall at 56 kph (35 mph) the described force limiter provides that the defined belt pullout allows a forward displacement of a 50%-er in a direction towards the steering wheel of about 30 cm.
If however the vehicle occupant is not a 50%-er but for example a 5%-er female, that is to say a female of a body weight of about 50 kg and 1.50 m tall (that is to say only 5% of all females are shorter and lighter), the force limitation at a value of 4 kN is not appropriate to keep the loading caused by the belt within tolerable limits.
In order to keep the loading caused by the belt tolerable for vehicle occupants of different heights and different body weights, for example DE 196 04 483 C1 proposes detecting the body data of a vehicle occupant and ascertaining the belt pullout allowed by the force limiting device, on the basis of the detected body data. However the operation of ascertaining the body data of a vehicle occupant is complicated and is not always reliable.
Therefore the object of the invention is to provide a method of establishing belt pullout in an occupant restraint system for vehicles, with which in the event of an accident the loading on a vehicle occupant by the safety belt can be limited substantially independently of the body data of the occupant.
A further object of the present invention is to provide an occupant restraint system for vehicles, with which in the event of an accident the loading on a vehicle occupant by the safety belt can be limited substantially independently of the body data of the occupant.